Zero intermediate frequency is a type of radio demodulation in which a mixer stage is used to convert an incoming signal to/from the baseband without generating an intermediate frequency. A zero intermediate frequency (ZIF) radio contains a local oscillator (LO) and a down-converter. The output of the local oscillator typically leaks into the input of a mixer. This generates an undesired DC component at the mixer output. The ZIF radio contains circuitry to cancel out this DC component. A measurement algorithm supplies the circuitry with compensation values, one set for each radio RF gain setting, since that setting affects the level of DC seen at the radio output.
In determining the compensation values, the algorithm ensures only the radio generates the undesired DC component by configuring it to minimize any input signal, typically by disconnecting the antenna from the receive path. For low gain settings (high attenuation), disconnecting the antenna can provide sufficient input isolation to calculate the compensation values. For higher gain settings (low attenuation), however, disconnecting the antenna usually does not provide sufficient input isolation in the presence of large power interferers when determining the calibration.
Thus, there is a need for a ZIF radio that overcomes the shortcomings of the prior art.